1. Field of the Invention
The present invention relates to the field of electrochemical devices having at least one electrochemically active layer capable of reversibly and simultaneously inserting ions and electrons, in particular electrochromic devices. These electro-chemical devices are, in particular, used to manufacture windows whose optical and/or energy transmission or optical reflection can be modulated using an electric current. They can also be used to manufacture energy-storage elements such as batteries or, alternatively, gas sensors or display elements.
2. Description of the Background
Considering the particular example of electrochromic systems, it will be recalled that, as is known, they include a layer of a material capable of reversibly and simultaneously inserting ions, in particular cations, and electrons, and whose oxidation states corresponding to the inserted and deinserted states are of distinct coloration, one of the states generally being transparent. The insertion or deinsertion reaction is controlled by a suitable electrical power supply, in particular by applying an appropriate potential difference. The electrochromic material, in general based on tungsten oxide, thus needs to be brought into contact with a source of electrons, such as a transparent electroconductive layer, and a source of ions, such as an ionic-conductor electrolyte.
It is furthermore known that, in order to provide at least of the order of a hundred switching operations, a back electrode which is itself also capable of reversibly inserting cations, symmetrically with respect to the layer of electrochromic material, must be associated with the layer of electrochromic material, so that, macroscopically, the electrolyte appears as a simple ion medium.
The back electrode must be formed either by a layer which has neutral coloration, or one which is at least transparent when the electrochromic layer is in the uncoloured state. Since tungsten oxide is a cathodic electrochromic material, that is to say its coloured state corresponds to the most reduced state, an anodic electrochromic material such as nickel oxide, iridium oxide or vanadium oxide, without implying any limitation, is generally used for the back electrode. It has also been proposed to use a material which is optically neutral in the oxidation states in question, for example cerium oxide or organic materials such as electronic conducting polymers (polyaniline, etc.) or Prussian blue.
Such systems are described, for example, in European Patents EP-0,338,876, EP-0,408,427, EP-0,575,207 and EP-0,628,849.
These systems can currently be divided into two categories, according to the type of electrolyte which they use:
either the electrolyte is present in the form of a polymer or a gel, for example a protonic-conduction polymer such as those described in European Patents EP-0,253,713 and EP-0,670,346, or a polymer with lithium-ion conduction such as those described in Patents EP-0,382,623, EP-0,518,754 or EP-0,532,408
or the electrolyte is an inorganic layer which is an ionic conductor but electronically insulating, in which case the term xe2x80x9call solidxe2x80x9d electrochromic systems is used.
Reference may be made to patents EP97/400702.3 of Mar. 27, 1997 and EP-0 831 360 for the description of an xe2x80x9call solidxe2x80x9d system. It is principally to this type of system that the invention relates, because it has a clear advantage in terms of ease of manufacture. This is because, with such a configuration, all the layers of the system can be deposited successively on a single carrier substrate (whereas in the system in which the electrolyte is a polymer or a gel, it is normally necessary to manufacture two xe2x80x9chalf-cellsxe2x80x9d which are assembled together via the electrolyte, which actually requires the use of two carrier substrates and the running of two series of layer depositions in parallel on each of them).
Whatever the configuration adopted, one requirement with this type of electrochemical system consists in giving it a xe2x80x9cmemory effectxe2x80x9d which is sufficient in terms of the application in question. This term is intended to mean the capacity which the system has to stay in a given state once the electrical power supply has been cut. In the case of an electrochromic window, this state is generally its coloured state. In the absence of an electrical power supply, it tends to revert to its uncoloured state. The aim is clearly for this memory effect to be able to last as long as possible so that, by means of the electrical power supply of the system, the user can actually control its state satisfactorily. In practice, it is for example desirable for the electrochromic window to be able to stay in the coloured state, with the power off, for several hours, for example 10 to 20 hours.
In practice, this goal is difficult to achieve because the system has to deal with a leakage current from one electroconductive layer to the other, in particular at the periphery of the system, which tends to make it revert to its equilibrium state, that is to say to its uncoloured state.
A first solution consisted in accepting the existence of these leakage currents, and in re-supplying the system with electricity when it is in its coloured state, with a given periodicity, in order to compensate for them. It is not, however, fully satisfactory, if only because these leakage currents can vary from one window to another, and in this case the coloration achieved by two similar windows supplied with electricity in the same way is different.
A second solution consisted in putting a margin on one of the two electroconductive layers, that is to say depositing the layers in such a way that they are offset at their periphery, and thus in eliminating/reducing the leakage current from one layer to another at their respective peripheries. The solution is effective but makes the process of manufacturing the system more complicated: in particular, it makes it necessary to deposit at least one of the two electroconductive layers by using a mask on the carrier substrate.
The object of the invention is therefore to overcome these drawbacks by providing, in particular, a novel method of processing the electrochemical devices described above in order to improve their performance, very particularly in order to limit/eliminate the risks of short-circuits, the so-called leakage currents and, thereby, in order to increase their xe2x80x9cmemory effectxe2x80x9d, and to do so while favouring simplicity in its implementation.
The invention firstly relates to a method of processing an electrochemical device having at least one carrier substrate provided with a stack of functional layers comprising at least one electrochemically active layer which is capable of reversibly and simultaneously inserting ions and electrons and which is arranged between two electroconductive layers. It is, in particular, an electrochemical device of the electrochromic type, with a stack of functional layers including at least, successively:
a first electroconductive layer,
a first electrochemically active layer capable of reversibly inserting ions, for example cations such as H+, Li+ or anions such as OHxe2x88x92, in particular of an anodic (or cathodic, respectively) electrochromic material,
an electrolyte layer,
a second electrochromically active layer capable of reversibly inserting the said ions, in particular of a cathodic (or anodic, respectively) electrochromic material,
a second electroconductive layer.
The method of the invention is characterized in that the functionality of at least one of the functional layers, with the exception of one of the electroconductive layers, in particular with the exception of the first (the one closest to the carrier substrate), is locally inhibited so as to delimit an inactive peripheral region in the stack.
In the context of the invention, the term xe2x80x9clayerxe2x80x9d is intended to mean either unitary layers or the superposition of a plurality of layers which jointly fulfil the same function. This is, in particular, the case with the electrolyte layer, which may consist of two or three superposed layers, as disclosed for example by the aforementioned patent EP97/400702.3.
Still in the context of the invention, the stack of layers may also comprise other layers, in particular protective layers, barrier layers, or layers with an optical or bonding function.
The benefit of the invention resides in the simplicity of its implementation, further to its effectiveness. This is because the method allows the layers to be processed once they are (all) deposited in a standardized way, without having to carry out selective deposition of layers, with mask systems or the like in order to obtain a xe2x80x9cmarginxe2x80x9d or an offset, for example. The invention is therefore particularly beneficial in the case of stacks of functional layers containing only layers of solid material: (the xe2x80x9call solidxe2x80x9d systems mentioned above).
In the context of the invention, the term xe2x80x9csolidxe2x80x9d material is intended to mean any material having the mechanical strength of a solid, in particular any material which is essentially inorganic or hybrid, that is to say partially inorganic and partially organic, such as the materials which can be obtained using a process of deposition by sol-gel synthesis.
In fact, in particular in the case of such an all-solid system, all of the layers can be deposited one after the other on the carrier substrate, preferably with the same deposition technique, on the same production line (in particular deposition by magnetic field-assisted sputtering), then all of the stack apart one of the electroconductive layers can be processed according to the invention. Of course, the invention also comprises the alternative variant consisting in stopping the deposition process, and in processing only some of the stack already deposited, then in continuing the deposition of the xe2x80x9cmissingxe2x80x9d layers in order to form the xe2x80x9cfullxe2x80x9d stack. (In the case of a system which is not xe2x80x9call solidxe2x80x9d, the xe2x80x9cmissingxe2x80x9d layers may be added by assembling the substrate with a second substrate, itself functionalized appropriately).
Keeping one of the electroconductive layers intact, unaffected by the inhibition process according to the invention, makes it possible to ensure correct supply of electricity to the terminals of the device. There are a variety of possible ways of maintaining this integrity for them, and these will be explained below.
The object of this local xe2x80x9cinhibitionxe2x80x9d of the stack of functional layers is to deactivate the device at its periphery, over a border a few millimetres wide, for example, so that in this periphery the system remains permanently in its least ionically and/or electronically conducting state (uncoloured state for most electrochromic systems). This xe2x80x9cinactivexe2x80x9d border is not in itself disadvantageous because its dimensions can be controlled and it can thus be concealed with ease, if this is deemed necessary from an aesthetic point of view, by the fitting, framing and peripheral-seal system of the device which is always present, very particularly when it is an electrochromic window.
This border actually equates to intentionally cutting the electrical circuit at the periphery of the system, thus eliminating any risk of short-circuit due to the current flowing between the two electroconductive layers. In the extreme, the electrical circuit may be cut by inhibiting only one of the electrochemically active layers exhibiting reversible insertion and/or the electrolyte layer and/or one of the electroconductive layers at their peripheries. However, as mentioned above, it is simpler to process all of the stack apart from the first layer. It should be noted that short-circuits are, in particular, due either to direct contact between the two electroconductive layers, or indirectly via one of the electrochemically active layers when these turn out also to be electronic conductors in one of their states (inserted or uninserted). Thus, tungsten oxide is a better electronic conductor in its coloured state, the same being true of nickel oxide and iridium oxide.
The invention provides two main variants for obtaining this localized-inhibition effect.
The first variant consists in locally inhibiting the functionality of at least one of the layers by cutting it (them) over its (their) thickness(es) along a closed line making it possible to delimit the inactive region of the stack between the said closed line of the edge/side of the stack (assuming all of the stacks, or the majority of them, have similar dimensions and/or are exactly superposed on one another. In fact, the first electroconductive layer usually has slightly larger dimensions than all the others, in order to make it easier to electrically connect it to the second layer, which allows the required connection elements to be placed on its surface which xe2x80x9cprotrudesxe2x80x9d from the stack.
This cut makes it possible to obtain a groove which breaks the circuit as explained above and leaves the periphery of the device unpowered.
Preferably, the cut is made along a closed line which, in smaller proportions, has a profile similar or identical to that of the edge of the stack (or of the edge of the first layer which experiences the cutting, if the underlying layers are of slightly different dimensions, in particular the first as indicated above). This provides an inactive border which xe2x80x9cfollowsxe2x80x9d the perimeter of the device and is easy to hide.
Advantageously, the cut is made by some mechanical means, in particular a cutting means, or by laser irradiation. One embodiment consists in leaving the device stationary during the processing and in fitting the mechanical means/laser emitter on a moving part, and another embodiment consists in doing the opposite.
Other means may also be used for making the cut by abrasion. For example, a means emitting a jet of gas or liquid under pressure (nitrogen, air), or a means emitting abrasive particles (glass or corundum beads, shot, solid CO2 beads, etc.).
This cutting operation may be carried out equally well whether the system is in the coloured or uncoloured state. When it is carried out using a laser beam, it may be beneficial to choose a coloured state, in order to increase the laser absorption by the stack at the wavelength used.
The second variant consists in locally inhibiting the functionality of at least one of the layers of the stack (always with the exception of one of the electroconductive layers) by degrading it (them) at its (their) periphery(ies), in particular by a suitable heat treatment or by suitable laser irradiation.
In this figurative case, the degradation is preferably carried out not along a closed line, like the cut according to the first variant, but over the entire surface of the peripheral border which it is desired to xe2x80x9cdeactivatexe2x80x9d thus.
Heat treatment or laser treatment have proved very effective in modifying the layer(s) in question sufficiently in terms of their chemical composition or their structure, in order thus to make them inactive. This is degradation in all likelihood involving, for example, dehydration and/or structural modification (in particular by crystallization) of the layer in question at least partially, without eliminating it.
It is rather beneficial to carry out this degradation treatment on the stack of layers when it is in its uncoloured state: this is because it is in this state that layers of the electrochromic type are least electronically conducting.
It can be seen that irradiation with a laser light can be used either in the context of the first variant, causing actual localized ablation, or in the context of the second variant, doing no more than modifying it. Their accuracy and their effectiveness make lasers particularly beneficial, it then being sufficient to modulate their operating parameters, as will be explained in detail below.
It is thus possible, in the scope of the invention, to make a plurality of closed peripheral cut lines, each closed line having a parameter smaller than the one which is adjacent to it and closer to the edge of the stack than it, and being contained in the xe2x80x9cinteriorxe2x80x9d area of the stack delimited by it (the successive closed lines may thus be concentric).
The same is true regarding the variant in which degradation is carried out: it is possible to make not one peripheral degraded region but several, for example concentric ones which may or may not be separated from one another by an unprocessed stack portion.
It should be noted that the two variants described above are alternative or cumulative. It is thus possible, in particular, to make a peripheral cut line and furthermore degrade the region which lies between the said line and the edge of the stack.
Moreover, it is also possible according to the invention to locally inhibit the functionality of at least one of the functional layers, with the exception of one of the electroconductive layers, so as to delimitan xe2x80x9cinactive contoursxe2x80x9d or a non-peripheral xe2x80x9cinactive regionxe2x80x9d in the device.
This inhibition may be carried out using one or other of the two variants explained above, namely either by localized degradation or localized ablation of the layer or layers in question, using the same means, namely heat treatment, laser treatment or some cutting means.
This operation may have two different purposes. It may firstly make it possible to reduce/eliminate non-peripheral short-circuits in the stack when the device is in operation, by deactivating the regions where point defects lead to electrical contacts between the two electroconductive layers, the regions thus rendered inactive being very small and therefore not very or not at all noticeable. In order to make these regions even less noticeable, arrangements may be made, once the regions have been processed, to colour them permanently using an ink jet of a dark colour close to that of the system in the coloured state. The xe2x80x9ccorrectedxe2x80x9d regions are therefore completely masked when the system is in the coloured state (the state in which points remaining bright would be most noticeable). It is thus possible easily and effectively to correct the point defects of the system.
This operation may also make it possible to draw patterns in the device, these patterns appearing only when the system is in its coloured state. It is thus possible, according to the way in which the degradation or ablation is carried out, to obtain patterns which are xe2x80x9csolidxe2x80x9d or delimited by contours as desired.
It has been seen above that the preferred embodiment of the invention consisted in the processing method affecting all of the functional layers apart from the (first) electroconductive layer. In order to preserve the latter""s integrity, its deposition parameters may advantageously be selected in order to make it more resistant, harder and denser than the other layers and, in particular, than the other electroconductive layer. The characteristics of the layer are thus modulated in combination with those of the means used for the processing so that the layer is not modified.
If this layer is, for example, deposited by magnetic field-assisted sputtering, it is possible, in a known way, to modulate its density by varying the pressure in the deposition chamber, the deposition temperature, etc.
It is thus possible to vary the deposition techniques used. For example, the layer which it is desired to preserve may be deposited by a hot deposition technique of the pyrolysis type (in the solid, liquid or gas CVD phase), well-suited to obtaining doped metal oxide layers and known to make it possible to obtain particularly hard and resistant layers, and depositing some or all of the other layers by a deposition technique which does not generally make it possible to achieve such high hardnesses, such as a vacuum deposition technique (sputtering, evaporation).
The invention also relates to the electrochemical device of the electrochromic type processed using the method described above, which has at least one peripheral inactive region remaining permanently in the uncoloured state, in particular in the form of a margin with a width of, for example, at most 5 mm.
The device processed according to the invention preferably has, during operation (in the coloured state), a leakage current (total leakage current per unit length of the perimeter) less than or equal to 20 xcexcA/cm, in particular less than or equal to 10 xcexcA/cm or 5 xcexcA/cm.